UBM Tech
UBM Tech

Tricolor LEDs create a flashing array

Jeff Tregre,, Dallas, TX; Edited by Martin Rowe and Fran Granville -June 24, 2010

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 LEDs create a flashing array figure 3You can build a matrix of RGB (red/green/blue) LEDs using a simple and inexpensive circuit comprising the control logic and driver circuit in Figure 1 and some LEDs (Figure 2). The center RGB LED is the first to come on, after which each sequential LED in the 8×8-LED matrix follows. This process gives the appearance that the display is alive and moving outward. This sequence repeats, producing a rainbow effect of colors.

You can adjust the frequency of each clock by changing the values of R17, R19, and R23. Use different frequencies for each clock, which will display eight colors from the 65 Tricolor
 LEDs create a flashing array figure 4tricolored LEDs, because using the same frequencies for all the clocks causes your display to appear white. The cost of building this circuit should be $25 to $30. You can purchase 100 5-mm RGB LEDs from eBay for a total of about $18. Be sure to use common- cathode LEDs.

This simple circuit comprises three clocks and three counters, one for each of the three LED colors. Setting each clock frequency to a different rate causes each color of each LED to appear to be random. All resistors are 0.25W, except for R3, R8, and R13, which are 0.5W; R4, R9, and R14, which are 1W; and R5, R10, and R15, which are 1.5W resistors. These high-wattage resistors and the 12 NPN transistors are necessary because all LEDs in this matrix, except the center one, connect in parallel. Start by bending all of the ground leads flat and connecting them together. When wiring the LEDs, begin in the Tricolor
 LEDs create a flashing array figure 5center and work outward. You can then mount the LED board onto the top of the PCB (printed-circuit board). Figures 3-7 and this video show the circuit in action. See Table 1 for a parts list.

To add the finishing touches to your project, use a small picture frame and install waxed paper onto the inside of the glass. Mount the LED board ¼ to 1 in. away. The magnifying lens of the LEDs will produce a beautiful effect when they shine through the waxed paper.
Tricolor   LEDs create a flashing array 
figure 6
Tricolor LEDs create a flashing array figure  7
 Table 1 Parts List
C1, C4, C6
C2, C3, C5
C7, C8, C9
LED1Red Indicator
LED2Green Indicator
LED3Blue Indicator
65 Common Cathode RGB LEDs
R1, R2, R6, R7, R11, R12, R18, R21, R24
R3, R8, R13
500Ω, ½W
R4, R9, R14
500Ω, 1W
R5, R10, R15
500Ω, 1½W
R16, R20, R22
R17, R19, R23
50k Servo Pots
U1, U2, U3

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